1. Clear WindowsXP / 2003 system password
Win7 system disk to boot the system imaging tool in the start menu provides a "system user login password change" tools 
take advantage of this "system user login password change" tool can easily remove Windows XP / 2003 system the user's password.
After running the tool, the first to enter the serial number [1], select the partition where the SAM file. 
Then the software will list all partitions in the system, which is partition number 0 is the C drive. Reference herein to continue to input [0]. 
To clear user input password number, where the input [0], remove Administrator user's password. 
Select an action to perform on the user's password, [X] represents selected. Here select "clear the user password" and press "Y" key to save your changes. 
Then you will be prompted to change the attributes success, reboot the system, Administrator user's password is cleared.
2. Clear Windows7 / 2008 system password
for security enhancements made Win7 system, so this "system user login password change" tool for Win7 system is invalid. Then you can use the WinPE CD's system tools included with the "Windows user password removal tool" to clear the user's password.
In the CD boot screen, select the "Start WinPE CD system." After entering the WinPE system, found on the desktop and run the "user password removal tool."
First, enter the Windows system in the "Select Target Path" column installation path "C: \ Windows", then select "Modify an existing user's password" on the left side of the "Select a Task" list item. 
For the administrator user "administrator" to reset a password, and select "Apply" in the list "a select operation" on the left. 
Tip password has been successfully updated, then click on the "OK" button, restart the system and found that the administrator user password has been changed.